According to Ghostery, you can disable this "messaging system".

Still, it's a bit concerning. Ghostery has long walked a fine line, serving both end users' privacy and advertisers' needs. Their most important asset might be user trust; nobody has the time a skill to learn what Ghostery's add-on is really doing. This move seems to suggest they are willing to risk that trust, as they appear to have no problem converting their privacy add-on into a private ad network. Users may wonder what's next, and what else is happening that they don't know about.

Also, does this change violate any Mozilla add-on rules? Users installed this add-on to limit the effects of advertising (i.e., tracking); using the add-on to send ads, even if only Ghostery promotions, is a major change.